"They find it difficult to interact with people, they don't pick up on social cues, they lack empathy, they make bad judgements... People with FTD become very gullible and they often part with large amounts of money," he added.

The research involved groups of FTD patients and Alzheimer's sufferers being shown skits played by actors. The same statements would be made deadpan, then again with heavy sarcasm.

The Alzheimer's patients would generally understand the difference, but the change was lost on those afflicted with FTD.

"One of the things about FTD patients is that they don't detect humour... patients with FTD are very literal and they take what is being said as genuine and sincere," said Hodges.

The research is regarded as medically significant because doctors often find it difficult to tell the difference between FTD and other mental illnesses.

The AFP reporters apparently asked Hodges whether the test would still work on "people from countries not renowned for their appreciation of sarcasm or irony".